Agricultural harvesting for many different tree crops is accomplished through inertial trunk shaking. Exemplary crops include almonds, pistachios, prunes, olives and walnuts, to name a few. With inertial trunk shaking, a portion of the machine, called the “shaker head” is clamped onto the trunk or a major scaffold of the tree. Then eccentric weights are made to spin and generate inertial forces that transfer vibration into the tree. The vibration travels up the tree and through the branches, ultimately causing the product to detach and fall either to the ground or to a catching frame. For many crops and in many places this practice has replaced hand-harvesting methods, which are costly and challenging for growers. The practice also helps optimize the use of land area. Realizing these benefits makes growers more competitive in the global market.
One challenge that faces operators of this equipment is the appropriate tuning of this system to best remove product while minimizing damage to the tree; a challenging balance because these are diametrically opposed optimization targets. Currently, this challenge is addressed primarily “in the lab” (or probably in a workshop), through trial and error, where a reasonable baseline speed, or frequency, is established through various gearing techniques. Since one wants to optimize the frequency to be close the right natural frequencies of the tree, lab optimization begins to improve the frequency issue, but for simplicity of design, existing machines typically work with two eccentrics that are in a fixed ratio relationship to that baseline frequency. This ratio is typically a function of non-adjustable gearing, which means that even with the small changes to the baseline frequency that a change to the engine throttle might produce, the ratio of the speeds stays fixed. This leads to the second challenge: optimization of output geometry.
The geometric position output of a shaker head (in the horizontal plane) that has a single, spinning eccentric is a simple ellipse. When two eccentrics are spinning at different frequencies, this ellipse changes to be a trochoid. In general, the equation that governs the output position of the head (working from a simplified, free-body-diagram point of view), is shown below:x(t)=E1 cos(F1*t)+E2 cos(F2*t)  (Eq. 1)y(t)=E1 sin(F1*t)+E2 sin(F2*t)  (Eq. 2)Fb=F1−F2 Er=E1/E2 Fr=F1/F2 Wherex(t) is the horizontal position of the head (in the horizontal plane) as a function of timey(t) is the vertical position of the head (in the horizontal plane) as a function of timeE1 is the eccentricity of the first eccentric (with dimension mass*length)E2 is the eccentricity of the second eccentric (with dimension mass*length)F1 is the frequency of the first eccentric (with dimension time−1)F2 is the frequency of the second eccentric (with dimension time−1)t is timeFb is the beat frequency (difference in the constituent frequencies)Er is the eccentricity ratio (dimensionless)Fr is the frequency ratio (dimensionless)
For linear actuators, E1 and E2 may be functions of time. This can be accomplished by varying the magnitude of the travel (peak-to-peak) of the moving mass. For a given frequency, as one increases the peak-to-peak magnitude of travel, the output will also increase. This also leads to nearly arbitrary output geometry and super-positioned frequencies, since there is no restriction that physics imposes any more to have a sinusoidal output per axes. X(t) and Y(t) become nearly arbitrary, though there are practical limitations for the length of travel of each actuator and for the mass/frequency combinations that result in force/power output limitations. For example, at any given time the actuator could deliver varying forces at a given frequency or vary frequencies at a given force. But, because of the inertial properties of the mass at the end of the linear actuator and the total travel capability of the actuator and the maximum speed of the actuator and the internal actuator force limitations, the actuator itself will be bounded only, it will have upper and lower bounds for those forces. In the same way, the output geometry size will have maximum bounds and the output frequencies will have minimums and maximums related to the same parameters.
The shape of the trochoid (not the absolute size) can be completely determined by the ratio of eccentricities and the ratio and sign of frequencies. Since a typical machine has fixed eccentrics and (as already described) fixed frequency ratios, the geometric position output of a typical head does not vary at all, regardless of the baseline frequencies and size of the eccentrics.
FIG. 1 depicts examples of trochoid shapes based on different frequency ratios. With Er fixed at the value of 1.6667 and Fr, varied, FIG. 1 depicts the resulting variety of trochoid shapes generated.
Each tree, as a complex mechanical structure, is unique in its vibratory transmission characteristics. Good cultural practices in pruning and consistency in treatment tend to yield statistically similar trees in a given block but this really depends on many other factors that are out of control of the grower, such as soil-type distribution throughout a given block. Additionally, hand-pruning is usually carried out by manual laborers, who vary significantly in their judgment calls as to what constitutes a wise choice for pruning cuts (and pruning cuts dictate much of the vibratory transmission characteristics). Soil moisture levels change constantly due to environmental factors such as weather and water availability, which changes the characteristics of the effective fulcrum formed by the ground and the trunk. Root structure varies significantly, which also changes how “soft” that ground-trunk fulcrum behaves. Furthermore, as a tree grows the mechanical properties of the wood change with age, as well as the size and geometry of the tree.
Year-to-year crop loads change dramatically, and different crop loads require different types of frequencies and geometries. In short, there is such vast variability from tree to tree that existing shakers often shake much harder than they need to, and shake at the wrong frequencies and wrong geometries—dumping unnecessary energy into the tree. This energy is lost in other forms (other than kinetic energy at the product), typically in short or long-term damage to the tree (e.g., root damage, trunk damage, scaffold/branch damage, defoliation, etc.). In addition, some of the crop is often left on the tree, which for the grower is literally unrealized profit.
Lastly, a tree's mechanical system changes as a shake is taking place because the crop is being removed, which changes the tree's mass distribution and the natural frequencies. The mechanical system also changes because the roots are moving in the ground, which changes how the soft fulcrum behaves. Different crops types and ages of trees evolve their dynamic state at different rates and have different safe envelopes.
It is not impossible to change the gearing of a typical shaker head: new sheaves, pumps, motors, etc., can be swapped in to create a new (albeit fixed) ratio. The problem with this is that it takes a large amount of time (often hours) to make this change just once. Such “tuning” of the shaker is very inefficient and time-expensive. In the middle of a harvest, time is money. Therefore, there is a disincentive to take the time (money) to try and make adjustments to a shaker head once a user feels that they are close enough.
For example, a typical tuning is usually performed “at the shop” and accomplished by changing the combination of gears, sprockets, pumps, motors, etc. Such tuning is not typically performed in the field. The small amount of tuning that is done in the field generally amounts to the following: tuning the eccentrics (typically two different eccentrics—e.g., changing their weights and manually setting a fixed speed ratio between the two), and either setting a fixed engine RPM level, or figuring out the sequence of how to move the throttle pedal to get the response wanted (very rough).
However, the typical tuning is unsatisfactory for a number of reasons. For example, tuning by way of engine throttle does not tune each eccentric individually, since they are each turning at a fixed ratio to the engine RPM. Tuning by way of varying the throttle via a pedal or lever, also does not allow a consistent, transient response—if the user is supposed to follow a shaking procedure by changing the engine throttle with their foot, it is very hard to make that procedure repeatable. Manually setting a fixed engine speed does not allow a user to take advantage of their real-time perception of how a tree responds to a particular shaking procedure. Setting a fixed or manual speed does not allow any intuitive sense or feel for the pattern, which is critical in converging upon an optimal shaking pattern without an automated solution. And, as discussed, the process is time-consuming. Other methods are very slow, while this method can literally be in real-time.
In the United States, there are three major players in the inertial trunk shaker space for fruit and nut harvesting. These systems typically feature a self-propelled chassis, a carriage, a shaker head with a two-jaw clamping system. They typically feature a two-eccentric system driven by a single motor coupled by belts and sprockets of different diameters to accomplish the fixed frequency ratio.
Orchard Machinery Corporation (OMC) is located in Yuba City, Calif. and produces a wide range of equipment for the orchard. Their current website address is www.shakermaker.com. They currently produce side-by-side systems (Magnum Catchall VII Series II), monoboom systems (Magnum Monoboom Series V), side-mount systems (Magnum Sprint Series V) and umbrella systems (Catchall V).
Orchard-rite Ltd., Inc. is located in Yakima, Wash. and produces several models, all targeted at nut shaking in particular. Their current website is www.orchard-rite.com. They produce a side-mount system (The Bullet) and a monoboom system (The MonoBoom).
Coe Orchard Equipment is located in Live Oak, Calif. and produces a variety of different equipment. Their current website is www.coeshakers.com. They produce a side-by-side system (The C7-E Shaker and L2-E Receiver), a side-mount system (S7 Side Mount Shaker) and a monoboom system (The M7 Mono Boom Shaker).
Therefore, there exists a need for a tree harvesting technology that can easily modify key characteristics of its shaker head to provide more optimal tuning to accommodate different trees and changing conditions. Those elements in question are the head's frequencies, specifically the individual frequencies themselves and in combination, the ratio between them.